Not applicable.
Not applicable.
1. Field of Invention
The present invention relates to the field of oil field drilling equipment. More specifically, the invention relates to a three-cone rock bit using a non-plugging center jet nozzle with a plurality of side passageways that are situated in a staggered fashion to prevent balling, or packing of the drill bit.
2. Related Art
In the drilling of oil wells, drilling fluid, or mud, provides lubrication, cooling, and cleaning by high pressure jets for the drill bit and provides for removal of the cuttings from the well bore. The mud circulates down through a drill string, into the drill bit body, typically through three nozzles positioned within the drill bit, and toward the bottom of the well bore. Nozzles are particularly useful because the relatively high-pressure mud creates high velocity jet streams within the hole and stir up formation cuttings, thus facilitating their circulation and removal from the well bore. From the well bore bottom, the mud circulates back to the surface carrying formation cuttings from the well bore. The process of removing the cuttings away from the bit and the efficiency with which it is accomplished is an important factor in determining the rate of penetration of the drill bit and, thus, the efficiency of the drilling. Therefore, increasing the efficiency of the removal of the cuttings increases the drilling efficiency.
Typically, drill bits define a void between and above cutter cones. Drilling mud and formation cuttings often accumulate within the void between and above cutting surfaces, thereby forming a mud ball that becomes impacted. This process, or phenomenon, of accumulation and impacting is generally referred to as xe2x80x9cballingxe2x80x9d or xe2x80x9cpacking off.xe2x80x9d Balling reduces the efficiency of the drilling process because a portion of the bit known as the dome (area above cutter cones) is packed off, causing the rotary cutter cones to become locked. This causes rotary cutter cones to skid on the bottom of the hole, therefore, slowing the rate of penetration. Thus, the drill bit and components should be designed to avoid balling.
The past benchmark for curtailing bit balling has been the installation of a fourth jet in the center of the bit (dome area). In the prior art, a single stream of drilling mud passing through the dome area of the bit provided some relief toward eroding a bit ball. However, additional improvements are needed in this area to reduce bit balling and thus improve efficiency per foot drilled. A multi-ported jet nozzle is needed to clean a larger area of dome and to reach those portions of bit domes inaccessible to the stream of a single port nozzle. Prior to the present invention, a design dilemma existed with respect to center-jet nozzles attempting a plurality of sideports (with more than one jetting stream). Namely, in a drill bit typically employing three nozzles and a fourth center jet nozzle, flow to the center jet nozzle is limited by virtue of flow to other nozzles. Therefore, multi-ported nozzle holes on a center jet are necessarily smaller so as not to unduly diminish drilling mud flow to other non-center jet nozzles. The design dilemma with such smaller holes in multi-ported center jet nozzles is that they cannot be run in a normal drilling operation because of the risk of their becoming plugged with impediments typically present in drilling mud. When plugging of these smaller holes in the central nozzle occurs, the usefulness of the center jet is compromised. The present invention solves this problem, thus enabling the use of small orifices to be run in a multi-ported nozzle without becoming plugged.
Accordingly, the objectives of the present invention are to provide an improved drill bit that:
provides greater drilling efficiency than previous drill bits;
provides greater cleaning for drill bit cutting surfaces;
provides a reduction of balling within the dome of rotary drill bits;
provides a reduction of mud and debris accumulation in the drill bit void and on cutting surfaces;
eliminates clogging of drill bit nozzles;
utilizes a nozzle with a plurality of side passageways (multi-ported);
provides an internal nozzle cavity (central passageway) shape that facilitates a constant drilling mud (fluid) velocity within the nozzle and that prevents clogging of side passageways by particles in the drilling mud;
utilizes descending tapered shapes within the nozzle to maintain velocity of drilling mud as drilling mud is injected through the nozzle, thereby preventing clogging of side passageways by particles in the drilling mud;
utilizes side passageways in the nozzle strategically situated at staggered heights on the nozzle body, and situated at varying angles, upward and downward to maximize cleaning, minimize balling, and increasing drilling efficiency;
utilizes a main exit aperture on the multi-ported nozzle of sufficient size to avoid plugging, thereby ensuring that the side passageways will remain unobstructed;
utilizes a central position of the nozzle within the drill bit;
and that uses a range of drilling mud injection velocities into the nozzle, so that clogging is reduced within the nozzle and so that the nozzle best sustains wear from injection of drilling mud, and particularly for preventing damage within the nozzle at the point where the central passageway meets the inlet orifices to the side passageways.
To achieve such improvements, the present invention generally provides a three cone rock bit, incorporating a non-plugging center jet nozzle fixed along a vertical central axis of the drill bit body and above the cutter cones. In general, the nozzle has a main inlet aperture, a main exit aperture, and a central passageway extending between the inlet and exit apertures. Side passageways intersect the central passageway and provide a bore through the nozzle sidewall through which drilling mud exits. Typically, inlet orifices to the side passageways are staggered vertically at different heights along the nozzle sidewall defined by the descending central passageway. Each of the side passageways also has an exit orifice occurring at an exterior surface of the nozzle.
The nozzle of the present invention includes a top, a bottom, a central passageway, sidewall, and central vertical axis. A central passageway extends from the top to the bottom of the nozzle in an axial direction so that the cavity formed by the central passageway also defines a sidewall of the nozzle that preferably varies in thickness depending on the width of the central passageway. The central passageway defines an inlet aperture at the top of the nozzle, and a main exit aperture at the bottom of the nozzle. The nozzle also defines a plurality of side passageways extending through the sidewall intermediate the top and bottom of the body and with the side passageways in fluid communication with and intersecting the central passageway which has conical or other tapering shape descending to the main exit aperture.
In the preferred embodiment, a non-plugging nozzle is centrally positioned along a vertical central axis within a rotary drill bit. The drill bit has a first end comprised of a bit body adapted for connection to a drill string and a second end of the bit delimiting a cutting surface formed by a plurality of rotary cutter cones. The drill bit defines at least one void formed between and the rotary cutting devices (cutter cones). The nozzle of the present invention extends into the void, or drill dome, above the cutter cones. This center nozzle includes means for functionally connecting to and remaining in fluid communication with the drill string. The nozzle directs drilling mud from the drill string through the bit and toward target voids and cutter cones. The rotary cone drill bit has a connecting means, or pin, at the upper end of the drill bit body that connects the rotary cone rock bit to a drill string. Preferably, the connecting means, or pin, is sized and constructed to mate with the drill string. Forming the lower end of the drill bit body are a plurality of leg segments, preferably three. Rotatably mounted to each of the leg segments, a rotary cutter cone extends inwardly toward the vertical axis of the bit body. The cutter cones are conical and have a base end and an apex end. The diameter of a rotary cutter cone decreases from the base end to the apex end. The base end of each rotary cutter cone is mounted proximal a leg segment. Therefore, with a plurality of rotary cutter cones so mounted, a void, or dome is defined between the rotary cutters and above the rotary cutting surfaces. Extending longitudinally into the drill bit body from the upper end, an opening passageway provides fluid communication with the drill string. This passageway typically extends through a top portion of the bit body in an axial direction, thereby keeping the drill string in fluid communication with all nozzles in the bit. In fluid communication with the opening, one multi-ported center jet nozzle (hereinafter xe2x80x9cnozzlexe2x80x9d or xe2x80x9ccenter-jet nozzlexe2x80x9d) directs drilling mud from the opening in a way that facilitates washing and reduction of balling within the drill bit dome, or void. The center-jet nozzle is attached within the opening passageway by connecting means and is positioned centrally above or lateral the cutter cones to direct drilling mud primarily toward the drill bit dome, well bore, and cutter cones. Preferably, the center-jet nozzle is positioned central along the drill bit vertical axis. The nozzle comprises a top end, bottom end, sidewall, and central vertical axis.
In the same embodiment, a longitudinal central passageway extends from the top end of the nozzle to the bottom end. The upper end of the central passageway has a diameter that decreases in the downward direction and toward the nozzle bottom. The nozzle attaches within the opening passageway of the drill bit by connecting means which are typically threadably screwing, or whereby the nozzle is locked down within the opening passageway. When the nozzle is attached to the drill bit, the nozzle is in fluid communication with the opening passageway. Drilling mud enters the opening passageway, moves through the inlet aperture of the nozzle, through the central passageway, through side passageways, and exits the nozzle through the main exit aperture and exit orifices (of the side passageways). Typically, the nozzle axis is vertically aligned and sharing the drill bit vertical axis. To provide for acceleration of the fluid (mud) from the cavity, the cross-sectional area (true flow area) of the main exit aperture of the nozzle is preferably greater than the cross-sectional area of at least one exit orifice concluding a side passageway on the nozzle.
The nozzle of the preferred embodiment contains a plurality of side passageways extending from the central passageway and through the nozzle sidewall. Such passageways of the nozzle are preferably positioned and adapted to produce a jetting of fluid (mud) toward the void of the drill bit and to produce a cross jetting of fluid through the void so that cuttings will not accumulate in the void, well bore, and on cutter cones. The cross jetting alleviates balling and plugging in the void. Side passageways in the nozzle typically have a constant diameter throughout their length defining cylindrical bores through the sidewall of the body. Alternately, side passageways may define an oval or slit shape throughout their length, thereby being adapted to create a fanning spray of drilling mud, thus lessening damage to cutting surfaces, which can be occasioned by high impact, tight jetting streams. Preferably, the shape of side passageways is constant throughout the entirety of side passageway length. To provide for side jetting, the side passageways extend through the nozzle sidewall at an angle perpendicular to the axis of the body or preferably at an angle of between ten and one-hundred-seventy degrees relative to the vertical axis. The range of angles allows the side passageways to direct fluid in an upward or downward direction as well as perpendicular to the axis of the drill bit. In the same preferred embodiment, side passageways are positioned on the body of the nozzle so that the inlet orifices of the side passageways are staggered in their placement on the central passageway. Staggering of inlet orifices along the central passageway is beneficial as it maintains the velocity of drilling mud through the central passageway. Side passageways draw on drilling mud flowing through the central passageway to produce side jetting. Thus, as drilling mud progresses through the nozzle, velocity of drilling mud moving through the central passageway will be inconsistent if inlet orifices leading to side passageways are randomly placed. However, properly spaced staggering of inlet orifices leading to side passageways along a descending taper shaped central passageway allows drilling mud to maintain substantially consistent velocity as drilling mud volume is channeled through side passageways selectively. Where staggered orifices are in place, velocity of drilling mud progressing through the nozzle has an opportunity to back up to its initial velocity before a subsequent inlet orifice draws on the volume of drilling mud within the central passageway. Consistent velocity within the central passageway is needed to maintain flow and to curtail small impediments in the drilling mud from plugging in the smaller inlet orifices leading to side passageways of the nozzle. This velocity will also cause temporarily obstructing particles and impediments in the drilling mud to be worn and washed away by fluid action, therefore reopening the small side passageways (side jets) in a short period. In this embodiment, the central passageway of the nozzle has a conical taper shape descending to the main exit aperture. This main exit aperture will be of sufficient size to avoid plugging, therefore permitting maintenance of central passageway velocity of drilling mud. The main exit aperture has a diameter of at least {fraction (8/32)} inches. Preferably, the main exit aperture has a diameter in a range of {fraction (8/32)} to {fraction (20/32)} inches. A descending tapering shape of the central passageway additionally maintains velocity of drilling mud within the central passageway, despite the existence of a plurality of staggered side passageways directing flow of the drilling mud in various directions. Functionally applying the above described apparatus provides a method of reducing mud accumulation in the dome of the rock bit and on cutter cones, thereby, improving the effectiveness of the center jet nozzle.
A second embodiment of the center jet nozzle has the same limitations of the first nozzle, however, the central passageway of the nozzle defines a sectional descending shape. The sectional descending passageway maintains fluid velocity within the nozzle central passageway, as does the tapered passageway defined by the first embodiment, however, further providing a sectional contoured shape that facilitates movement of drilling fluid and which further resists clogging of side passageways by kicking small impediments toward the center of the cavity. Volume of fluid passing through this central passageway decreases with the shape of the passageway, consequently, fluid velocity is maintained in the central passageway, despite the presence of a plurality of staggered side passageways which draw on fluid (drilling mud) flowing through the central passageway.
The first and second embodiments of the present invention are optimally realized by propelling drilling mud through the central passageways at velocities causing minimal damage to nozzle components and which are most likely to avoid clogging of side passageways. Accordingly, the present invention provides for methods of using the rotary drill bit and contained non-clogging nozzles wherein drilling mud within the central passageway is optimally propelled at a velocity in the range of 75 to 300 feet per second as measured within the nozzle central passageway.